The use of brines in workover and completion fluids in oil field operations is well known to those skilled in the art. Workover fluids are those fluids used during remedial work in a drilled well. Such remedial work includes removing tubing, replacing a pump, cleaning out sand or other deposits, logging, etc. Workover also broadly includes steps used in preparing an existing well for secondary or tertiary recovery such as polymer addition, micellar flooding, steam injection, etc.
Completion fluids are those fluids used during drilling and during the steps of completion, or recompletion, of the well. Completion operation can include perforating the casing, setting the tubing and pump, etc. Both workover and completion fluids are used in part to control well pressure, to stop the well from blowing out while it is being completed or worked over, or to prevent the collapse of casing from over pressure.
Chemicals are added to the brines for various reasons that include, but are not limited to, increasing viscosity, reducing corrosion, and increasing the density of the brine. For example, in order to obtain a brine having a salinity of about 14.5 to 15.5 pounds per gallon, zinc bromide is often added to the brine. Chemicals such as, for example, water-thickening polymers serve to increase the viscosity of the brines, when used as workover fluids or completion fluids, to retard the migration of the brines into the formation and to lift drilled solids from the wellbore.
A variety of water-thickening polymers have been used to increase the viscosity of brines that do not contain zinc compounds. Examples of such water-thickening polymers include hydroxyethyl cellulose, carboxylmethylhydroxyethyl cellulose, carboxymethyl cellulose, polysaccharides such as xanthan gum, and polyacrylamide. However, these polymers do not viscosify, or increase the viscosity of, brines that contain zinc ions in the range of 0.1% to 7%. Because zinc compound-containing brines are widely used as workover fluids or completion fluids in oil field operations, development of a process for viscosifying the brines is highly desirable.